NFL Network's Tom Pelissero reports that players will undergo a second weigh-in shortly before they do on-field drills. For example, a receiver who weighed in on Monday will do so again on Thursday afternoon before their drills to ensure they're testing at their listed weight.
The committee general managers formed to consider changes requested the second weight due to the extended time at the combine and the gap between a player's initial weigh-in and workout day. Similar to a pro day, Pelissero was told, it is important to know the weight on the day of a workout.
The tweak is just another detail of what has been a recent overhaul of the combine. This year marks the first in which the event will be televised live on prime time, and with new drills being added, the event continues to improve itself in more ways than one.